2,4-bis(isocyanatocyclohexylmethyl) cyclohexyl isocyanate

ABSTRACT

THE TRIISOCYANATE 2,4-BIS(4-ISOCYANATOCYCLOHEXYLMETHYL) CYCLOHEXYL ISOCYANATE IS PREPARED BY PHOSGENATING THE CORRESPONDING TRIAMINE. THE TRIISOCYANATE IS USEFUL IN THE PREPARATION OF POLYURETHANE MATERIALS.

United States Patent 3,557,180 2,4-BIS(ISOCYANATOCYCLOHEXYLMETHYL)CY'CLOHEXYL ISOCYANATE Guenther Kurt Hoeschele, Wilmington, Del.,assignor to E. I. du Pont de Nernours and Company, Wilmington, 'Del., acorporation of Delaware No Drawing. Filed July 2, 1968, Ser. No. 741,847Int. Cl. C07c 87/42, 119/04; C0821 22/28 US. Cl. 260-453 1 ClaimABSTRACT OF THE DISCLOSURE The triisocyanate 2,4 bis(4isocyanatocyclohexylmethyl) cyclohexyl isocyanate is prepared byphosgenating the corresponding triamine. The triisocyanate is useful inthe preparation of polyurethane materials.

BACKGROUND OF THE INVENTION Polyisocyanates are highly useful compoundswhich have gained wide acceptance as starting materials for themanufacture of useful products such as foams and coating materials. Theisocyanates most extensively used are the aromatic diisocyanates suchas2,4-tolylene diisocyanate (or a mixture thereof with 2,6-tolylenediisocyanate) and 4,4'-methylene bis(phenol isocyanate), or crudemixtures containing the above isocyanates and various by productsproduced during the manufacture of the isocyanates.

Polymers prepared from aromatic polyisocyanates have a tendency todiscolor on aging. For applications in which discoloration isundesirable, a non-discoloring aliphatic isocyanate can be used.Examples of known aliphatic polyisocyanates are 1,6-hexamethylenediisocyanate, 4,4- methylene bis(cyclohexyl isocyanate) and1,3-cyclohexylene diisocyanate.

Though many of the known aliphatic isocyanates are more or less suitablefor use in preparing such products as polyurethane coatings and foams,there is a need for an aliphatic isocyanate which has a functionality(isocyanato groups per molecule) greater than two. Isocyanates having ahigher functionality generally yield faster curing coatings which aretougher and more stable against outdoor exposure and certain solventsthan coatings prepared from lower-functional isocyanates. Foams preparedfrom higher functional isocyanates generally develop gel strength morerapidly and manifest improved compression set. Other highly desirableattributes of any isocyanate are low volatility (and thus low toxicity)and liquidity at normal operating temperatures for ease of storage andhandling. Few, if any, of the known aliphatic isocyanates combine allthese desirable attributes.

SUMMARY OF THE INVENTION This invention provides the new aliphatictriamine, 2,4- bis(4-aminocyclohexylmethyl)cyclohexylamine, and thecorresponding triisocyanate, 2,4-bis(4-isocyanatocyclohexylmethyl)cyclohexyl isocyanate. Novel polyurethanecompositions prepared by reacting said triisocyanates withactive-hydrogen containing compounds are also provided.

3,557,180 Patented Jan. 19, 1971 DETAILED DESCRIPTION The triisocyanateof this invention corresponds to the following structural formula:

replaced by amino groups. The triamine is a viscous liquid boiling atabout 198 C. at 1 mm. Hg.

The starting material for the triamine is the corresponding aromatictriamine. The aromatic triamine is prepared by condensing aniline andformaldehyde by the procedure disclosed in the following representativereferences: 'U.S. Pats. 2,818,433, 2,974,168 and 3,163,666. Aniline andformaldehyde are reacted in the presence of a mineral acid. Hydrochloricacid is preferred, although other mineral acids, such as sulfuric acid,can be used. While the exact amount of acid to be used is notparticularly critical, the practical range is between about 0.4 and 2moles per equivalent of amine. The preferred range is about 0.81.0 molesper equivalent of amine. The mineral acid will, of course, form saltswith the amines present and it is to be understood that the term mineralacid is meant to include salts of the acid with the amine. Also, theaniline which reacts with formaldehyde can be present as the free amineor as a salt of the mineral acid.

As is well known, the condensation of aniline and formaldehyde asdescribed above produces a mixture of methylene-bridged polyphenylenepolyamines which include 4,4-methylenedianiline (MDA),2,4-bis(4-aminobenzyl)aniline (the desired aromatic triamine startingmaterial) and related higher polyamines. The relative proportions ofthese amines in the reaction product de' pends on the ratio of anilineto formaldehyde used. In order to maximize the yield of aromatictriamine, the aniline-formaldehyde ratio should be at least 2.011 andpreferably about 2.8-3.0:1, though higher and lower amine/formaldehyderatios can be used.

After the reaction is complete, unreacted aniline and methylenedianilineare removed by distillation, and the crude 2,4 bis(4-aminobenzyl)anilinefurther purified by distillation. The aromatic rings of the triamine arethen hydrogenated by conventional procedures, illustrative of which isthe method described in US. Pat. 2,606,925. Alternatively, thedistillation residue remaining after removal of MDA can be hydrogenateddirectly without isolation of the aromatic triamine, and thecycloaliphatic triamine can then be isolated from the mixture ofhydrogenated materials. The ring hydrogenation of the aromatic triamineproceeds smoothly to high yields of the aliphatic triamine substantiallyfree of aromatic amines.

The cycloaliphatic triamine is a complicated mixture of various possiblestereoisomers. The related diamine, 4,4'-methylene bis(cyclohexylamine),exists in three stereoisomeric forms, and the presence in the compoundof the third aminocyclohexyl group increases the number of possiblestereoisomers to sixteen. The ratio of the various stereoisomeric formswill vary to a considerable extent with the exact conditions used incarrying out the hydrogenation. For discussion of the variations ofstereoisomeric forms of the diamine see US. Pat. 2,494,- 563, column 1.

To obtain the corresponding triisocyanate, the triamine is phosgenatedusing conventional methods such as those described in US. Pats.2,818,433,2,974,168, 3,163,666 and 3,367,969. The conversion of thetriamine to the triisocyanate does not affect the structuralconfiguration and therefore the isomeric ratio of the triamine issubstantially carried over to the isocyanate.

The triisocyanate and its mixtures with other aliphatic polyisocyanates,particularly 4,4'-methylene-bis(cyclohexyl isocyanate) can be reactedwith at least one activehydrogen containing compound, i.e., polyols,polyamines and water, to prepare non-discoloring coatings, adhesives andflexible foams by methods well known in the art. In coating and adhesiveformulations, the triisocyanate can be used to replace tri'functionalaromatic isocyanate components. The inherently lower reactivity ofaliphatic isocyanates can be compensated by the use of catalysts. Inpreparing non-discoloring flexible foams, the triisocyanate ispreferably used in admixture with an aliphatic diisocyanate. Whileflexible foams can be prepared from such mixtures by a one-shotprocedure, prepolymer and quasi-prepolymer procedures are preferredbecause of the relatively low reactivity of aliphatic isocyanates.Tetramethylguanidine is a preferred catalyst for the reaction ofaliphatic isocyanates with water.

The usual polyether and polyester diols and polyols can be employed inpreparing coatings, adhesives and foams based on the triisocyanate;however, polyesters are often preferred because of their greaterresistance to oxidation which complements the non-disooloringcharacteristics of the aliphatic isocyanates. Representative polyolsuseful in this invention are given in US. Pat. 3,248,373 to Barringer.Detailed information on formulations and procedures for preparingrepresentative urethane coatings, adhesives and flexible foams can befound in Chapters VII, X and XI of Polyurethanes: Chemistry andTechnology, Part II, Saunders and Frisch, Interscience Publishers(1964).

The triamine is useful as an intermediate in the preparation of thetriisocyanate. The triisocyanate is highly useful in the preparation ofsuch materials as polyurethane coatings and foams as described above. Ithas the important advantage of being a liquid at room temperature andthus is conveniently handled and stored. The triisocyanate has extremelylow volatility which is a significant factor with respect to safety topersonnel handling the material. Because of the known structure of thetriisocyanate, it provides a convenient means of controlling the averagefunctionality of reactants to be used in polyurethane preparation. Afurther advantage of the triisocyanate is that it contains oneisocyanato group which is less reactive than the other two (attached tothe central carbocyclic ring) which is important in certain applicationswhere it is desired to leave some isocyanato groups available forfurther reaction, e.g., moisture-cured coatings.

The invention will be further illustrated by the following exampleswherein parts and percentages are by weight unless otherwise indicated.

EXAMPLE I (a) Preparation of 2,4-bis(p-aminobenzyl)aniline- Aniline andformaldehyde are reacted in the presence of hydrochloric acid usingmolar ratios of aniline to formaldehyde of about 3:1 and aniline to HClof about 0.92:1. The reaction is carried out first at 20-42 C. and thencontinued at about 65 C. for about 4 hours. The reaction mass is addedto aqueous sodium hydroxide to neutralize the amine hydrochloride. Theaqueous and organic phases are separated, and unreacted aniline isdistilled off leaving a crude reaction mass containing about 85.7%4,4'-methylenedianiline. 3346 grams of this crude product are distilledat a pressure of 0.5 mm. Hg to remove most of the methylenedianiline,leaving a residue of 477 g. 467 Grams of this residue are transferred toa smaller flask and distillation is continued. After discarding 37 g. ofa forerun, a total of 335 g. of distillate is collected (pot temperatureof 290340 C. at 0.5 mm. Hg) and 92.5 grams of residue remain in theflask. The distillate is recrystallized twice from toluene, and theproduct is further purified by continuous extraction with n-hexane for 4hours to remove any trace of methylenedianiline. The purified compound,2,4-bis(p-aminobenzyl)aniline, melts at 133-135 C.

Analyses for amino nitrogen show the following:

Calcd for C H N (percent): 13.85. Found (percent): l3.7, 13.9.

(b) Preparation of 2,4-bis (aminocyclohexylmethyl)cyclohexylamine.Thecompound prepared in paragraph (a) above is hydrogenated as follows:

A mixture of ml. of dioxane, 50 g. of anhydrous ammonia, 15 g. ofcatalyst comprising 5% ruthenium on finely divided alumina, and 100 g.of 2,4-bis (p-aminobenzyl)aniline is hydrogenated in a reactor pressuredwith hydrogen at 5000 p.s.i.g. at 210 C. for one hour, with agitation.The reactor is cooled and vented, and the product is rinsed from thereactor with dioxane. The dioxane solution is freed of catalyst byfiltration and is distilled to yield2,4-bis(4-cyclohexylmethyl)cyclohexylamine boiling at 198 C./ 1 mm. Hg.The product is a clear, colorless syrup. The distilled triamine has an ramine equivalent weight as determined by titration with standard acidsolution, of 107.7 (calculated, 107.2) and is substantially free ofaromatic material, as shown by ultraviolet analysis.

Analyses show the following:

Calcd for C H N (percent): C, 74.7; H, 12.23; N, 13.06; mol. weight,321.5. Found (percent): C, 73.7; H, 12.2; N, 12.8; mol. weight(cyroscopic in benzene) 331, 335.

(c) Preparation of 2,4-bis(4-isocyanatocyclohexylmethyl)cyclohexylisocyanate.A solution of 30 g. of the triamine prepared as described in(b), dissolved in 310 g. of dry o-dichlorobenzene, is saturated withanhydrous hydrochloric acid at 120 C. with eflicient agitation. Phosgeneis added to the resulting slurry at 165 C. for about 2 hours until ahomogeneous reaction mixture is obtained. The charge is swept withnitrogen to remove phosgene, and the solvent is distilled off underreduced pressure (20 mm. Hg) and finally at C. and 0.5 mm. Hg. The crudephosgenation product (35.4 g.) is purified by continuous extraction withpetroleum ether (boiling range 30-60 0.). About 1 g. of the crudematerial is insoluble in petroleum ether and discarded. The extractedproduct is freed of solvent by distillation yielding an almost colorlessviscous liquid.

Analyses show the following:

Calcd for C H N O (percent): C, 69.2; H, 8.33; N, 10.52; NCO (ASTMD163860T) 31.55; mol. weight (cryoscopic method in benzene) 399.5. Found(percent): C, 68.6, 68.5; H, 8.4, 8.3; N, 10.5, 10.4; NCO (AST MD-163860T) 30.95; mol. weight (cryoscopic method in benzene) 399, 407.

The structure of the 2,4-bis(4-isocyanatocyclohexylmethyl)cyclohexylisocyanate is confirmed by nuclear magnetic resonance and infraredspectroscopy.

EXAMPLE 2 Crude methylenedianiline, prepared as described in Example 1,is distilled at reduced pressure to remove methylenedianiline. Theresidue comprising 2,4-bis(paminobenzyl)aniline and minor amounts ofhigher poly amines is hydrogenated by the procedure described inExample 1. The aliphatic triamine is isolated from the reduction mass byfractional distillation at 1 mm. Hg in a spinning band column. About 70parts of triamine, substantially identical to that prepared in Example1, is obtained for each 100 parts of starting residue. The distilledtriamine is phosgenated according to the procedure of Example 1. Theproduct, after extraction with petroleum ether, is obtained with about90% yield based on the aliphatic triamine as a slightly yellowish clearliquid having an isocyanate content of 30.65%. A purer and completelycolorless product is obtained by distillation in a falling filmmolecular distillation apparatus (6 inches of heated column, mean freepath 2 mm.) at a pressure of 1 micron at a column temperature of 125-Analyses show the following:

Calcd. (percent): C, 69.2; H, 8.33; N, 10.52; NCO (ASTM D-l638-60T)31.55; mol. weight (vapor phase osmometry in benzene) 399.5. Found(percent): C, 69.1, 69.2; H, 8.3, 8.4; N, 10.3. 10.3; NCO (ASTM D-1638-60T) 31.1; mol. weight (vapor phase osmometry in benzene) 400.

EXAMPLE 3 A prepolymer is prepared by mixing 80 parts of a polyestertriol having an equivalent weight of about 1000 (obtained byesterification of adipic acid with a mixture of diethylene glycol andtrimethylolpropane) with 58 parts of a liquid mixture of stereisomers of4,4-methylenebis(cyclohexyl isocyanate) containing about 20% transtransisomer, 65% cis-trans isomer and 15% cis-cis isomer at room temperatureand heating the resulting mixture for 20 hours at 67 C. The resultingprepolymer has an isocyanato group assay of 10.6%.

Foam AA non-discoloring flexible foam is prepared from this prepolymerby a batchwise quasi-prepolymer procedure employing the followingformulation.

Parts Prepolymer 130.0 Triisocyanate of Example II 22.0 Polyester trioldescribed in this example 23.6 N,N-dimethylformamide 9.5 Methylenechloride 8.0 Silicone surfactant for flexible polyester foams sold byUnion Carbide as L-532. Described in L-532, Silicone Surfactant forPolyester Urethane Formation, Product Information Bulletin, UnionCarbide, 1966 1.5 Water 3.72 Tetramethylguanidine 4.0

The materials are added in the order shown at room temperature and theresulting mixture is agitated for about 12 seconds with a high-speedmixer and then poured into an open container and allowed to foam. Theformulation requires about 150 seconds to reach maxim-um height. Thefoam does not exhibit any shrinkage and has uniform fine cells. It has adensity of about 2.0 lbs./cu. ft. After aging for 20 hours at 120 C.,the foam has a compression set of 27% by ASTM Method B (50% compression,22 hours/ 70 C./30 minute recovery).

Foam B-A second foam is prepared by the same procedure with theexception that the 22.0 parts of triiso cyanate is replaced with achemically equivalent amount (34.3 parts by weight) of a 77% by weightsolution of the trimer of 4,4-methylenebis(cyclohexyl isocyanate)dissolved in 4,4'-methylenebis(cyclohexyl isocyanate). The isocyanateassay of the trimer solution is 19.7%. The trimer solution is preparedby heating 100 parts of the liquid 4,4'-methylenebis(cyclohexylisocyanate) previously described in this example in the presence of 2parts of 1,1,2,4,4,5,5-heptamethylisobiguanide at 60-70 C. until theisocyanate assay drops to the desired value The distillation apparatusused is described in Review of Scientific Instruments, v01. 31, No. 9,pp. 1002-1004 (1960).

and preventing further trimerization by the addition of 1 part ofbenzoyl chloride. Foam B reaches maximum height in about 120 seconds anddoes not exhibit any shrinkage. Its cell structure is somewhat coarserthan that of Foam A. After aging for 20 hours at 120 C. the compressionset of Foam B is 59, over twice the value found for Foam A by the sametest method.

Foam C-A third foam is prepared by substantially the same procedure usedfor Foam A with the exception that the 22.0 parts of triisocyanate isreplaced with a chemically equivalent amount (21.8 parts by weight) ofthe liquid 4,4'-methylenebis(cyclohexyl isocyanate) previously describedin this example. Foam C rises to maximum height in about 130 seconds,does not shrink and has uniform fine cells. After 20 hours aging at 120C. its compression set is about 60, again over twice that found for FoamA by the same test method.

EXAMPLE 4 (a) The triisocyanate product of Example 1 is mixed with anequal weight of the liquid 4,4-methylenebis(cyclohexyl isocyanate)described in Example 3. The resulting mixture, which has an isocyanatecontent of 31.3%, is used to prepare a coating composition as follows:

54 parts of the mixture is mixed with parts of a hydroxy-tenminatedpolyester diol having an equivalent weight of 265 and a hydroxyl No. ofabout 205 (the diol is the reaction product of adipic acid and arnixture of ethylene glycol and propylene glycol containing 70 molepercent ethylene glycol) and 154 parts of urethane grade butyl acetate.The NCO/OH ratio is 1:1. Dibutyl tin dilaurate is added (0.15 part). Theresulting solution has a workable pot life of 16-20 hours. Films arecast for determination of properties. For the hardness test 3 mil. thickfilms are cast on glass. For the evaluation of abrasion resistance andtensile properties wet films 20 mil. thick are cast on aMylar"[poly(ethylene terephthalate)] film. Cures are at room temperaturefor the time shown in the table.

TABLE Hardness (determined by Sward Rocker Cure: Sward reading 1 day 4 5days 24 10 days 28 For a discussion of the Sward Hardness Rocker seeOfllcial Digest, Federation of Paint and Varnish Production Clubs, 26,1030-8 (November 1954). The apparatus is available from the GardnerLaboratory, Inc., Bethesda, Md.

A brasz'on Resistance (determined by means of a Taber Abraser, CS-l7wheel, 1000 g. wt.)

Weight loss per 1000 Cure: revolutions, mg. 1 week 1 month 86 [StressStrain Properties (measured by ASTM Method D 412-621)] Tensile strengthElongation at break, at break, Cure p.s.i. percent 1 week 3, 500 1 month5,150 110 7 opposed to less than 1 day for the films of part (a). Thefilms are so soft that they have a Sward hardness of only 4 after 10days and are not suitable for the determination of stress-strain data.

(0) When films are prepared as in part (21) except using thetriisocyanate as the only isocyanate component and the samestoichiometric proportion of the polyester, the solution has a somewhatshorter pot life. The films prepared are harder and more resistant toweather exposure than those of part (a).

What is claimed is:

1. 2,4 bis (4 isocyanatocyclohexylmethyl)cyclohexyl isocyanate.

8 References Cited UNITED STATES PATENTS 6/1954 Seeger et al 260-4536/1957 Campbell et al 260453 0 D. H. TORRENCE, Assistant Examiner US.Cl. X.R.

